Flasher circuit with outage indication

ABSTRACT

A flasher circuit has a power transistor controlling a circuit with a load therein; a multivibrator produces a timed pulse signal applied to the power transistor for turning the power transistor &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39;; and additional current sensing means coupled to the load and sensitive to a reduction in the current flow therethrough, due to an outage, is operatively connected to the multivibrator for eliminating the timed occurrence of said signal.

United States Patent Bolinger 1 Feb. 29, 1972 [54] FLASHER CIRCUIT WITHOUTAGE 2,994,013 7/1961 Skellett ..331/113 X INDICATION 3,217,20711/1965 Webb ..317/33 B 3,253,186 5/1966 Rogers et a1. ..331/1l3 X 1lnvemofl John s" Mlchlsan Y 3,408,540 10/1968 Nield et al. ....317/14s.sB 7 Assigneez di -h fl Inc. southfield 3,551,744 12/1970 Keller et....3l7/333 R Primary Examiner-Johns. Heyman [2 Filedi y 1970Attorney-McGlyma, Reising, Milton 8!. Ethington, Martin J Adelman, AllenM. Krass, Owen E. Perry, Thomas N. Young [21] Appl. No.. 35,496 andStanley C Thorpe [52] US. Cl ..307/202, 307/240, 307/246, [57] ABSTRACT[5| 1 Int Cl 307/247 307/252 331/113 A flasher circuit has a powertransistor controlling a circuit [58] Fieid J with a load therein; amultivibrator produces a timed pulse 331/62 3l5/209 5 5 R 3 signalapplied to the power transistor for turning the power 148 5 R 5transistor on; and additional current sensing means coupled to the loadand sensitive to a reduction in the current flow therethrough, due to anoutage, is operatively connected to [56] References Cited themultivibrator for eliminating the timed occurrence of said UNITED STATESPATENTS Signal- 2,832,900 4/1958 Ford ..307/202 X 8 Claims, 1 DrawingFigure PAIENTEDFEB29 I972 INVENTOR. Jim ffiofz'zzgez BY v M fM ATTORNEYSFLASI'IER CIRCUIT WITH OUTAGE INDICATION BACKGROUND OF THE INVENTIONHeretofore various circuits have been proposed for use as flashercircuits. However, such flasher circuits have been, and often still are,susceptible to the occurrence of a particular lamp or bulb, within theoverall load, becoming burned out. Such occurrences can become dangerouswhere, for example, the flasher circuit is employed as a directionalturn indicator on motor vehicles or an emergency flashing system as onschool buses or the like, because the vehicle operator may not haveknowledge that a particular lamp or bulb is burned out and is assumingthat all pedestrians as well as other vehicles are aware that he issignaling his particular intent to perform a particular vehicularmaneuver.

Accordingly, the invention as herein disclosed and described is directlyconcerned with the solution of the above as well as other relatedproblems.

SUMMARY OF THE INVENTION According to the invention, a switching circuitcomprises electrical load means, a load circuit containing saidelectrical load means, first load switching means in circuit with saidload circuit, second means for cyclically producing a control signal forcausing said first switching means to be at times rendered conductive,and additional means responsive to the occurrence of an outage conditionin said load means and being effective in response thereto to preventthe said cyclic production of said control signal.

Various general and specific objects and advantages of the inventionwill become apparent when reference is made to the following detaileddescription considered in conjunction with the drawings.

DESCRIPTION OF THE DRAWINGS The single drawing is a schematic wiringdiagram of a flasher circuit employing the invention disclosed herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greaterdetail, the singe drawing illustrates a flasher circuit comprised of afirst conductor 12 having an end 14 suited for connection to a suitablesource of electrical potential 16 and a second conductor 26 which leadsto ground as at 28.

A signal producing portion 30 of the circuit 10 is illustrated ascomprising oscillator means composed of transistors 32 and 34.Transistor 32 has its collector electrode 36 connected in series with aresistor 38 leading to conductor 12 while its emitter electrode 40 isconnected to conductor 26. Transistor 34 similarly has its collectorelectrode 42 connected, in series with a resistor 44, to conductor 12while its emitter electrode 46 is connected, via conductor 48, to thebase electrode 50 of a third transistor 52 which, in turn, has itsemitter electrode 54 connected to conductor 26 via conductor means 27.

Base electrode 56 of transistor 32 is electrically connected,viaconductor S7, in series with one end of a resistor 58 which has itsother end adapted for connection to conductor 12 as through a switch 20.Similarly, base electrode 60 of transistor 34 is electrically connected,via conductor 62, in series with one end of a resistor 64 which has itsother end connected to conductor 12.

A first capacitor 66 has one end or side connected to a pointelectrically between resistor 38 and collector electrode 36 and theother end or side connected to conductor 62. A second capacitor 68similarly has one side connected to a point electrically betweenresistor 44 and collector electrode 42 of transistor 34 while its otherside is connected to conductor 57. Additionally, capacitors 70 and 71may be provided so as to have their respective one sides connected toconductors 57 and 62 while their respective other sides are connected toground through conductor 26.

The collector electrode 72 of transistor 52 is connected to a voltagedivider network comprised of conductors 74, 76 and 78 between which areserially connected resistors 80 and 82. Conductor 78 is connected toconductor 12 while the base electrode 84 of a fourth transistor 86 isconnected to a point generally between resistors 80 and 82 as at 88 onconductor 76. Transistor 86, which may be considered as a switchingtransistor, has its emitter electrode 90 connected to conductor 12 as bymeans of a conductor 92 while the collector electrode 94 thereof isconnected, via conductor 96, to the base terminal 98 of a power or loadswitching transistor 100 the collector 102 of which is connected toconductor 12 by means of conductor 104. A conductor 106, connected atone end to the emitter 108 of transistor 100, has its other endconnected to one end of coil means 110 the other end of which isconnected to a conductor 112 leading to related electrical load means114 which, in turn, is connected to ground as at 116. As shown, aresistor 118 has its opposite ends connected to conductors 96 and 106while resistor 120 has its opposite ends respectively connected toconductors 48 and 26.

The circuit 10 may also include short protection means comprised of ashutdown transistor 122 having its emitter 124 connected, through aresistor 126, to conductor 12 while its collector 128 is connected,through a resistor 130, to ground as by conductor 26. The base electrode132 of transistor 122 is connected, as by a conductor 134 and resistor136 in series therewith, to conductor 74 as at 138.

A silicon-controlled rectifier (SCR) 140 has its anode connected, viaconductor 142, to conductor 48, as at 144, while its cathode isconnected by means of a conductor 146,- which may include a diode 148serially arranged therewith, to conductor 106 as at 150. The gateelectrode 152 of SCR 140 is connected through a resistor 154 toconductor 156 leading between collector 128 and resistor 130.

Generally, in order to make an SCR conductive, forwardly, it isnecessary to apply a voltage across the anode to cathode terminals ofthe SCR (making the anode positive, with respect to the cathode) and atthe same time apply a voltage (or current flow) to the gate-to-cathodecircuit by making the gate positive, with respect to the cathode. Ofcourse, if after the SCR is made conductive, current flow from the anodeto cathode is interrupted, the SCR will again go into its nonconductivestate.

7 In addition to the above, a diode 158 may be connected to conductor106, as at 160, and to conductor 26, as at 162. Such a diode 158 hasbeen found to be desirable where the particular circuit employedexhibited high inductance whenever the load was turned off. Theprovision of such means as diode 158 serves to reduce suchcircuit-created high inductance at load turnoff.

Further, it has been found that a zener diode 164 and diodes 166 and 168are preferably serially provided in conductor means 27 when theassociated short protection means disclosed herein is employed. Diodes170 and 172 respectively connected in the base circuits of transistors32 and 34, although not essential to the practice of the invention, arenevertheless preferred in order to serve as voltage limiters for suchtransistors. In this connection, resistor 174, in series with conductor12, may also be employed as a means of reducing the line voltage to theoscillator or multivibrator section 30. Capacitors 70, 71 and 73 areprimarily provided as a means of noisesuppression in order to preventtransistors 32, 34 and 52 from going into conduction as a result ofstray signals.

OPERATION OF THE INVENTION In view of the above, it can be seen thateach of transistors, 32, 34, 52 and 100 are of the NPN type whiletransistors 86 and 122 are of the PNP type. Accordingly, during normalconduction, in the NPN type, the emitter will be negative with respectto both the collector and base while the collector is positive withrespect to both the emitter and base. In the PNP type, normal operationor conduction is achieved when the emitter is positive with respect toboth the collector and base while the collector is negative with respectto both the emitter and base.

Further, transistors 32 and 34 comprise a multivibrator the operation ofwhich is generally as follows. First, for ease of presentation, let itbe assumed that switch is nonexistant and that resistor 58 is connectedto conductor 12; further, assuming that a related control switch 175 isclosed, let it be assumed that transistor 32 has just switched on,creating current flow through the emitter-collector circuit 40, 36, andthat transistor 34 has switched off or to its nonconducting state. Itcan be seen that at this particular instant capacitor 66 was fullycharged and that the side thereof connected to resistor 64 was negativewith respect to the other side of capacitor 66 which is connected toresistor 38 and collector 36. The circuit through emitter-collectorcircuit 36, 40 is completed to ground 28 as by conductor 26. At thistime capacitor 68 will be discharged.

Capacitor 66 now starts charging toward the opposite polarity throughresistor 64 by virtue of being essentially connected to conductor 26when transistor 32 is conducting and the emitter-collector circuitthereof is completed. It can also be seen that because of the chargeexisting on capacitor 66, at the instant that transistor 32 went intoconduction, and its connection to base electrode 60 of transistor 34 viaconductor 62, the emitter-base electrodes of transistor 34 are reversebiased (the base being negative with respect to emitter 46) therebykeeping transistor 34 in an off or nonconducting state. At this sametime, capacitor 68 will start to charge essentially through theemitter-base circuit of transistor 32 and resistor 44. This chargingcurrent holds transistor 32 conductive or hard-on; further, even whencharging of capacitor 68 is completed, the transistor 32 will remainconductive by virtue of the base current provided by resistor 58.

As the potential across capacitor 66, holding transistor 34 off, isreduced, a condition is finally attained where the capacitor 66 voltagecan no longer maintain transistor 34 in the nonconducting state. Astransistor 34 starts to become conductive, by virtue of a biasingcurrent through resistor 64, the collector to emitter voltage thereofdrops and the charged capacitor 68 now starts to discharge through theemitter-base circuit of transistor 32, resulting in a reverse biasdriving transistor 32 into nonconduction.

When transistor 32 is thusly driven into nonconduction, the voltageacross its emitter 40 and collector 36 increases causing capacitor 66 toagain start charging through the emitterbase circuit of conductivetransistor 34.

In this new state (transistor 34 being conductive) capacitor 68 startsto charge toward the opposite polarity through resistor 58 by virtue ofbeing connected to conductor 26 through the conducting transistor 34.When transistor 34 was switched into conduction, capacitor 68 wasnegatively charged on its side connected to conductor 57, with respectto its side connected between resistor 44 and collector 42. Further, thepolarity on capacitor 68, at the time of switching transistor 34 on,produces a reverse bias on transistor 32.

During the time that transistor 34 is conducting capacitor 66 is beingcharged so that its end or side connected to resistor 64 and conductor62 will become negative with respect to its side connected betweenresistor 38 and collector 36. Such charging of the capacitor 66 is theconsequence of the base current flow through transistor 34 which alsoserves to hold the transistor 34 in its on or conductive state. Itshould be apparent that transistor 32 is also maintained conductive forsome period after capacitor 66 has been fully charged because of thebase bias provided by resistor 64.

However, as capacitor 68 continues to discharge and the voltagethereacross approaches zero, the voltage holding transistor 32 in anonconducting state decreases and transistor 32 starts to again becomeconductive. This initiates the regenerative cycle which results in therapid tum on of transistor 32 and tumoff of transistor 34 as well as thesubsequent rapid tumoff of transistor 32 and tum on" of transistor 34.In this arrangement resistors 38 and 44 serve to respectively limit thecollector currents of transistors 32 and 34 while resistor 64 andcapacitor 66 combine to determine the off" or nonconducting time oftransistor 34 and, similarly, resistor 58 and capacitor 68 combine todetermine the off or nonconducting time of transistor 32.

It can be seen that when transistor 34 is in its conducting state, theemitter-base circuit of transistor 52 is biased into conduction therebycompleting the circuit through the emitter 54 and collector 72 oftransistor 52. When transistor 52 is thusly driven into conduction, acircuit is completed through conductors 78, 76 and 74, collectorelectrode 72, emitter 54 and conductor means 27 causing a voltage dropto occur across resistor 82 thereby causing point 88 and base 84 to benegative with respect to emitter which is exposed to plus potential ofconductor 12. Consequently switching transistor 86 is turned oncompleting a circuit through the emitter 90 and collector 94 thereby,through conductor 96, placing the base electrode 98 of load or powertransistor 100 effectively at the plus potential of conductor 12. Theemitter 108 is, in turn, at negative potential of ground 116.Accordingly, with emitter 108 negative with respect to base 98,transistor 100 is turned on completing the load circuit comprised ofconductors 104, collector 102, emitter 108, conductor 106, coil 110 andconductor 112 so as to energize the electrical load means 114. As shouldbe apparent, the diagrammatically depicted load means 114 may in fact becomprised of, for example, one or a plurality of lamps or bulbs and, asis often the case, some of such bulbs could be located within theinterior of the vehicular passenger compartment, as operator signalreadouts, while others could be located externally of the vehicle asindicators to pedestrians and vehicular traffic.

In view of the preceding, it can be seen that, in the embodimentdisclosed, every time that oscillator or multivibrator transistor 34 isturned on the buffer transistor 52, switching transistor 86 and loadtransistor 100 are likewise turned on." The contrary is, of course,true; that is, whenever transistor 34 is in its off or nonconductivestate, transistors 52, 86 and 100 are also in their off or nonconductivestate.

Now, considering the short protection means, it will be remembered thatin order to make the SCR 140 conductive, both the anode and gate thereofhave to be made positive with respect to the cathode. Accordingly, itcan be seen that whenever the shutdown transistor 122 is off or in anonconductive state, the circuit described by conductor 176, resistor126, conductor 178, conductor 156 and resistor is open by virtue of noconduction through the emitter-collector circuit of transistor 122.Consequently, the gate electrode 152 of SCR will be at negative orground potential by virtue of its connection to conductor 156.

However, it will be noted that each time transistor 52 goes intoconduction base 132 of transistor 122 is effectively brought to groundpotential as at point 138 thereby causing transistor 122 to becomeconductive thereby completing the circuit through conductors 176, 178and 156. Gate 152 is therefore made positive by virtue of resistors 126and 130 acting as a voltage divider. However, SCR 140 does not go intoconduction because its cathode is effectively at positive potential byvirtue of its connection to conductor 106 as at which, because oftransistor 100 being on, is at the plus potential of conductor 12.

Now, let it be assumed that a short has occurred in the load 114 andthat transistor 34 has just turned on" which, as explained above, causesthe transistor 122 to be simultaneously turned on. Therefore, gate 152of SCR 140 is made positive and the cathode of SCR 140, by virtue of theshort in the load 114, is placed effectively at ground potential.Further, with transistor 34 being on the anode of SCR 140 is at sameplus value relative to its cathode. This, of course, as previouslyexplained, causes SCR 140 to become conductive completing a circuit frompoint 144 through conductors 142, 146 and 112.

When the SCR- thereby becomes conductive, the forward bias on thebase-emitter circuit of transistor 52 is eliminated or so reduced as toprevent transistor 52 from going to conduction which, in turn, preventstransistors 86 and 100 from being turned on" thereby eliminating thepossibility of damage to the load transistor 100 as a consequence ofsuch a short in the load.

As was previously stated, it has been found advantageous to providemeans such as the zener diode 164. That is, when SCR 140 is madeconductive, a voltage drop, in the order of possibly 1.0 volts, willoccur across the SCR 140. However, this voltage drop would also appearacross the base-emitter diode of the transistor 52 and would besufficient to cause the transistor 52 to become conductive. Accordingly,by including the zener diode 164 in the emitter circuit of transistor 52such possible tum-on" of the transistor will be positively preventeduntil the potential across the base-emitterzener becomes of a valuedistinctly in excess of the voltage drop across SCR 140 when in itsconducting state.

Having described the operation of the signal producing section 30 andthe nonnal load switching operation as well as the function andoperation of the related short protection means, the remaining circuitryand operation of the related outage indication means will now beconsidered.

The concern with the occurrence of shorts arises because of the loss ofeffective resistance in the load circuit; in contrast, with theoccurrence of an outage condition, at least some portion of theelectrical load is, for example, burned out and therefore such portionappears as an open switch in the cir cuit. Y

The operation of the circuitry remains the same as previously describedexcept that now switch is again considered as being in the locationillustrated, and operatively connected, as by means 180, to coil 110.(Switch 20 and winding 110 may, in fact, comprise a reed-type switchwherein member 20 is moved, without benefit of mechanical connections,to open and closed positions in response to the generation of anassociated magnetic field.)

Switch 20 can be considered as a normally open switch in the sense thatit will be open, as shown, whenever there is either no current flowthrough coil 110 orcurrent flow below a predetermined value.

Accordingly, when the associated master switch 175 is closed currentwill not be pennitted to flow through resistor 58 because of the openswitch 20; however, as previously described, current flow throughresistor 64 causes transistor 34 to be turned on" thereby causingtransistors 52, 86 and 100 to be also driven into conduction. If theload 114 is nor mal (no outage present) the current flow through winding110 will be sufiicient to cause switch 20 to become closed therebypermitting the oscillator or multivibrator to function normally, aspreviously described, causing the transistor 34 to be cyclicallyenergized.

However, should one or more of the individual loads 1140,

114b, or ll4c (if in fact the load 114 is comprised of a plurali-' ty ofloads) create an outage as by becoming burned out, the efiectiveresistance of the electrical load means will increase thereby reducingthe magnitude of the current flow therethrough as well as through thewinding or field generating means 110. Therefore, if the winding orfield generating means 110 is so constructed or calculated as to developsufficient force or energy to close switch 20 only when all of theelectrical loads in the load means 114 are normal, it-can be seen thenthat upon the occurrence of an outage in the load means, the currenttherethrough will diminish to a value less than a predetermined minimumvalue resulting in switch 20 again becoming opened and remaining open.

When this happens, the base circuit of transistor 32 loses its forwardbias and therefore remains in a nonconductive state while transistor 34becomes continuously forwardly biased through resistor 64 therebyremaining "on or in its conductive state. As a consequence of transistor34 being held on the remaining transistors 52, 86 and 100 are also heldon thereby serving to keep the normal electrical loads (the ones whichhave not burned out) in a continuously energized state which wouldindicate to the vehicle operator that an outage had occurred. A resistor182 arranged in parallel with capaci' tor 68 serves as a bleed resistorpermitting the capacitor 68 to be discharged therethrough wheneverswitch 20 is opened.

In view of the preceding, it should be apparent that functionalequivalents could be substituted for the various sections of thecircuitry as well as components or elements contained therein. Also, asshould be apparent, the circuitry disclosed could be practical employingNPN transistors for those that are shown as PNP and vice versa whereappropriate polarity changes are made as is well known in the art.

Although only one embodiment of the invention has been disclosed anddescribed, it should be apparent that other embodiments andmodifications of the invention are possible within the scope of theappended claims.

I claim:

1. A flasher circuit of the type adapted to intermittently energize asignal lamp load from a voltage source including an oscillator forproducing intermittent control signal impulses, a switching deviceadapted to be switched between on and off conditions in response to saidcontrol signal impulses to connect and disconnect the load and thevoltage source, the improvement comprising control means connected incircuit with said load and effective to change from a first condition toa second condition when the magnitude of the current through the loaddecreases below a predetermined value, said control means beingefiective in said second condition to hold said switching device in saidon condition whereby a decrease of said current below said predetenninedvalue causes the remaining signal lamps to be continuously energizedfrom said voltage source to indicate the outage of one of said signallamps.

2. The invention as defined in claim 1 wherein said control means is acurrent-responsive device having an input circuit connected with saidload circuit and an output circuit operatively connected with saidswitching device.

3. The invention as defined in claim 2 wherein said control meanscomprises a relay having an energizing winding in said load circuit andhaving switch contacts operatively connected with said switching device.

4. The invention as defined in claim 3 wherein said oscillator is amultivibrator comprising a pair of cross-coupled transistors and theswitch contacts of said relay are connected in the input circuit of oneof said transistors.

5. A flasher circuit for automotive vehicles and adapted tointermittently energize a load circuit including signal lamps from avoltage source, an oscillator for producing intermittent control signalimpulses, a switching device connected with the oscillator and adaptedto be switched between on and off conditions in response to theintermittent control signal impulses to connect and disconnect the loadcircuit and the voltage source, .first control means having an inputconnected across the load and having an output connected to theswitching device, said first control means being adapted to change froma first conductive state to a second conductive state when the voltageacross the input thereof decreases below a predetermined value and beingefiective in said second conductive state to hold said switching devicein said off condition to deenergize the load in the event of a shortcircuit, second control means having an input connected with the loadcircuit and an output operatively connected with said switching device,said second control means being adapted to change from a firstconductive state to a second conductive state when an open circuitoccurs in one of the signal lamps and the current through said loaddecreases below a predetermined value, said second control means beingeffective in the second conductive state to hold said switching devicein the on condition and continuously energize the remaining signal lampsin the load circuit.

6. The invention as defined in claim 5 wherein said first control meansis a voltage-responsive device and said second control means is acurrent responsive device.

tor is a multivibrator comprising a pair of crosscoupled transistors andthe switch contacts of said relay are connected to the input of one ofsaid transistors to hold the multivibrator in one stable state when thecontacts are closed.

1. A flasher circuit of the type adapted to intermittently energize asignal lamp load from a voltage source including an oscillator forproducing intermittent control signal impulses, a switching deviceadapted to be switched between on and off conditions in response to saidcontrol signal impulses to connect and disconnect the load and thevoltage source, the improvement comprising control means connected incircuit with said load and effective to change from a first condition toa second condition when the magnitude of the current through the loaddecreases below a predetermined value, said control means beingeffective in said second condition to hold said switching device in saidon condition whereby a decrease of said current below said predeterminedvalue causes the remaining signal lamps to be continuously energizedfrom said voltage source to indicate the outage of onE of said signallamps.
 2. The invention as defined in claim 1 wherein said control meansis a current-responsive device having an input circuit connected withsaid load circuit and an output circuit operatively connected with saidswitching device.
 3. The invention as defined in claim 2 wherein saidcontrol means comprises a relay having an energizing winding in saidload circuit and having switch contacts operatively connected with saidswitching device.
 4. The invention as defined in claim 3 wherein saidoscillator is a multivibrator comprising a pair of cross-coupledtransistors and the switch contacts of said relay are connected in theinput circuit of one of said transistors.
 5. A flasher circuit forautomotive vehicles and adapted to intermittently energize a loadcircuit including signal lamps from a voltage source, an oscillator forproducing intermittent control signal impulses, a switching deviceconnected with the oscillator and adapted to be switched between on andoff conditions in response to the intermittent control signal impulsesto connect and disconnect the load circuit and the voltage source, firstcontrol means having an input connected across the load and having anoutput connected to the switching device, said first control means beingadapted to change from a first conductive state to a second conductivestate when the voltage across the input thereof decreases below apredetermined value and being effective in said second conductive stateto hold said switching device in said off condition to deenergize theload in the event of a short circuit, second control means having aninput connected with the load circuit and an output operativelyconnected with said switching device, said second control means beingadapted to change from a first conductive state to a second conductivestate when an open circuit occurs in one of the signal lamps and thecurrent through said load decreases below a predetermined value, saidsecond control means being effective in the second conductive state tohold said switching device in the on condition and continuously energizethe remaining signal lamps in the load circuit.
 6. The invention asdefined in claim 5 wherein said first control means is avoltage-responsive device and said second control means is a currentresponsive device.
 7. The invention as defined in claim 6 wherein saidcurrent responsive device is a relay having an energizing winding incircuit with the load and having switch contacts operatively connectedwith the switching device.
 8. The invention as defined in claim 7wherein said oscillator is a multivibrator comprising a pair ofcross-coupled transistors and the switch contacts of said relay areconnected to the input of one of said transistors to hold themultivibrator in one stable state when the contacts are closed.